This application claims the priority of Korean Patent Application No. 2002-80060, filed on Dec. 14, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an apparatus and a method for reproducing a skin color in a video signal, and more particularly, to an apparatus and a method for improving the quality of reproducing a skin color in a video signal, with standardizing the value of a color difference signal in an a typical skin color (hereinafter called ‘atypical color’) area as the value of a color difference signal in a typical skin color (hereinafter called ‘typical color’) area, based on a memory color.
2. Description of the Related Art
The human optic nerve is very sensitive to skin color reproduced by a video display. Thus, human eyes immediately sense even a slight variation or abnormality when skin color is reproduced. For this reason, it is regarded that skin color reproduction capability greatly influences image quality of a display. There has been a great deal of research into optimizing reproduction of skin color. Further, as today's displays are digital, an image of high quality is required, and for this reason, optimization of reproduction of skin color is very important.
Prior art related to skin color reproduction includes a method for reproducing skin color by determining a skin-color-area using a color signal phase of an input image signal and phase shifting or adjusting amplitude of a color signal (U.S. Pat. Nos. 3,748,825, 3,729,578, 3,873,760, and 4,327,374), a method for reproducing skin color by adjusting average luminance as well as the phase and amplitude of a color signal (U.S. Pat. No. 5,585,860), and a method for reproducing skin color by determining a skin-color-area according to amplitude of a color signal and adjusting at least one of three color signals such as Red, Green, and Blue (U.S. Pat. Nos. 3,253,305 and 5,381,185). In these methods, operational convenience can be pursued, but the accuracy of determination of a skin-color-area, which is a premise of reproduction of skin color, is small. Thus, an adjustment object_color may not be a adjusted, or an adjustment non-object color may be adjusted.
Another prior art document discloses a method for reproducing skin color by detecting a skin-color-area using fuzzy modeling by hue, saturation, and luminance of a video signal and adjusting saturation and luminance of the video signal (U.S. Pat. No. 6,272,239). A one-dimensional skin-color model is used in this method. Thus, the accuracy of a skin-color-area is small, and an undesirable color may be adjusted.
Another prior art document discloses an approach that is different from the above-mentioned prior art. It discloses a method for reproducing skin color, in which a specific color of a typical color of skin is designated in advance in chromaticity coordinates, a square area within a proper range centering on the specific color is determined as a skin-color-area, and all colors within the square area are adjusted as the specific color (U.S. Pat. No. 5,384,501). This method has the following problems. First, a distribution of actual skin colors in chromaticity coordinates has a nearly circular or oval shape. But, in this method, the area of the skin color is determined as a square area. Thus, an adjustment non-object color may be adjusted, as in the above-mentioned technologies. Second, according to recent research results (entitled “Colour Memory for Various Sky, Skin and Plant Colour-Effect of the Image Context”, COLOR research and application, Peter Bodrogi, August 2001, No. 4, Vol. 26), a case where a color within a typical color area is not adjusted as a specific color is more suitable for human visual characteristics. In this method, even this case, all colors are adjusted as the specific color. Thus, reproduction quality of skin color may be lowered. In addition, the method comprises changing brightness of skin color into a specific and typical brightness value. In this case, brightness of a specific pixel may be lowered.